Ultraviolet and visible radiation is being increasingly used for a wide variety of applications in different industries. For example, ultraviolet radiation is used for the photopolymerization of liquid and solid polymers in the optical, semi-conductor, electronic, and medical industries, and is also used for the cleaning and etching of semi-conductors, metals and plastics, surface cleaning and etching, sterilization, exposing light sensitive materials, and illumination. In the chemical industry, ultraviolet radiation is used for, among other things, inducing reactions in gases, liquids and emulsions. Other commercial applications for ultraviolet radiation include the use thereof in relation to the photoexposure of films, photopaper, and photosensitive emulsions and materials. Ultraviolet radiation, alone or in combination with ozone, is also used for sterilization applications.
Prior art systems for generating ultraviolet or visible radiation typically comprise low-pressure mercury or fluorescent lamps which are powered with AC voltage through common fluorescent ballasts. These prior art radiation generating systems possess certain deficiencies which detract from their overall utility. Such deficiencies include the very large size and weight of the system due to the need to include a separate ballast for each lamp, and the high power consumption associated with the inclusion of many ballasts. Thus, although ultraviolet radiation can be used in numerous applications as described above, the prior art systems for generating ultraviolet radiation are highly inefficient, and costly to manufacture as well as to operate.
It has been determined in the prior art that the efficiency of excitation of electric discharge in a gas filled lamp can be increased up to two times by replacing the AC or DC excitation with microwave excitation. In addition to increasing discharge efficiency, the use of microwave excitation also eliminates the need for the ballasts to power each of the individual lamps. The use of microwave powered efficient, medium pressure mercury lamps is disclosed in U.S. Pat. Nos. 3,872,349, 3,911,318, and 4,042,850. In these particular references, microwave cavities are used in conjunction with microwave powered ultraviolet light sources. However, the microwave cavities disclosed in these references operate on fundamental or near fundamental cavity modes. These types of mode structures make it impossible to simultaneously excite a large number of lamps uniformly due to the inclusion of very clearly defined, non-homogeneous standing wave electric field distribution inside the microwave cavity. Though the multi-mode cavities widely used in conventional microwave ovens provide homogeneous electric field distribution inside the cavity, they do not provide the critical optimal electric field strength absolutely necessary for the efficient excitation of mercury, fluorescent or other types of gas discharge lamps for the efficient generation of ultraviolet radiation and/or visible radiation.
The present invention overcomes the deficiencies associated with the prior art by defining the critical conditions which interrelate the geometry of the microwave cavity, the individual lamp dimensions, the microwave cavity volume, and the microwave power of the magnetron generator for the efficient, homogeneous excitation in the same microwave cavity of from one to thousands of ultraviolet and/or visible light producing lamps for the production of ultraviolet and/or visible radiation. In the present invention, ultraviolet and/or visible radiation is generated with up to two times less energy consumption than prior art AC/DC mercury or other gas discharge lamp ultraviolet and/or visible radiation generators including the same number of lamps. In this respect, the present invention provides a powerful, compact, low-cost and reliable ultraviolet and/or visible radiation generator for the production of ultraviolet and/or visible radiation using standard, low-pressure mercury lamps or other types of UV or visible light producing lamps.